the scCheckout is an 'order' level event and should not go in the product string as per Adobe's definition.If you have a variable in the data layer that defines the shopping action eg. utag_data.shopping_action = 'checkout' then you could map this via tealium to the event scCheckout by simply using the Tealium UI. Check in the mapping dialog the events part and input the value of the shopping_action variable (eg. checkout) in the input field and select scCheckout from the dropdown. This should be working perfectly. Basically you are now telling Tealium that when the shopping_action variables value equals to checkout then the scChecout has to be set.